As a new biologically active peptide derived from brain hypothalami, testes or the like, polypeptide PACAP38 consisting of 38 amino acid residues have recently been discovered from sheep and humans. The amino acid sequence of PACAP38 is represented by formula I: ##STR1##
PACAP38 enhances the production of intracellular c-AMP in hypophysis cells and the production of c-AMP of astroglia cells, which, in turn, increases the survival time of nerve cells.
This activity of PACAP38 is also observed in PACAP-27-NH.sub.2 consisting of 27 amino acid residues on the N-terminal side of the peptide. Since PACAP38 has the DNA sequence corresponding to an amidation processing structure, -Leu.sup.27 Gly.sup.28 -Lys.sup.29 -Arg.sup.30 -, in the cDNA structure thereof, the above-described activity has previously been confirmed in the synthesized PACAP-27-NH.sub.2.
On the other hand, vasoactive intestinal peptide (VIP) is a peptide which is known to exist in the brains as a neurotransmitter or a nerve activator. PACAP-27-NH.sub.2 has 68% homology with VIP in amino acid sequence. However, VIP is very weak in c-AMP-producing activity.